With a recent trend toward higher integration and higher density in semiconductor devices, circuit interconnects become finer and finer and the number of levels in multilayer interconnect is increasing. In the process of achieving the multilayer interconnect structure with finer interconnects, film coverage of step geometry (or step coverage) is lowered through thin film formation as the number of interconnect levels increases, because surface steps grow while following surface irregularities on a lower layer. Therefore, in order to fabricate the multilayer interconnect structure, it is necessary to improve the step coverage and planarize the surface in an appropriate process. Further, since finer optical lithography entails shallower depth of focus, it is necessary to planarize surfaces of semiconductor device so that irregularity steps formed thereon fall within a depth of focus in optical lithography.
Accordingly, in a manufacturing process of the semiconductor devices, a planarization technique of a surface of the semiconductor device is becoming more important. The most important technique in this planarization technique is chemical mechanical polishing. This chemical mechanical polishing (which will be hereinafter called CMP) is a process of polishing a substrate, such as a wafer, by placing the substrate in sliding contact with a polishing pad while supplying a polishing liquid containing abrasive grains, such as silica (SiO2), onto the polishing pad.
This chemical mechanical polishing is performed using a CMP apparatus. The CMP apparatus typically includes a polishing table with a polishing pad attached to an upper surface thereof, and a polishing head for holding a substrate, such as a wafer. The polishing table and the polishing head are rotated about their own axes respectively, and in this state the polishing head presses the substrate against a polishing surface (i.e., an upper surface) of the polishing pad, while a polishing liquid is supplied onto the polishing surface, to thereby polish the surface of the substrate. The polishing liquid to be used is typically composed of an alkali solution and fine abrasive grains, such as silica, suspended in the alkali solution. The substrate is polished by a combination of a chemical polishing action by the alkali and a mechanical polishing action by the abrasive grains.
As polishing of the substrate is performed, the abrasive grains and polishing debris adhere to the polishing surface of the polishing pad. In addition, characteristics of the polishing pad change and its polishing performance is lowered. As a result, as polishing of the substrate is repeated, a polishing rate is lowered. Thus, in order to restore the polishing surface of the polishing pad, a dressing apparatus is provided adjacent to the polishing table.
The dressing apparatus typically includes a dresser having a dressing surface which is brought into contact with the polishing pad. The dressing surface is formed by abrasive grains, such as diamond particles. The dressing apparatus is configured to press the dressing surface against the polishing surface of the polishing pad on the rotating polishing table, while rotating the dresser about its own axis, to thereby remove the abrasive grains and the polishing debris deposited on the polishing surface, and to planarize and condition (or dress) the polishing surface.
Each of the polishing head and the dresser is a rotating body that is rotated about its own axis. When the polishing pad is rotated, undulation may occur on the surface (i.e., the polishing surface) of the polishing pad. Thus, in order to enable the rotating body to follow the undulation of the polishing surface, a coupling mechanism that couples the rotating body to a drive shaft through a spherical bearing, is used. Since the coupling mechanism allows the rotating body to be tiltably coupled to the drive shaft, the rotating body can follow the undulation of the polishing surface.
However, when the dresser is pressed against the polishing pad, a relatively large moment due to a frictional force is exerted on the spherical bearing. As a result, the dresser may flutter or vibrate. In particular, as a diameter of a wafer becomes larger up to 450 mm, the flutter or vibration of the dresser is more likely to occur, because a diameter of the dresser also becomes larger. Such flutter or vibration of the dresser inhibits appropriate dressing of the polishing pad. As a result, uniform polishing surface cannot be obtained.
Japanese Laid-Open Patent Publication No. 2002-509811 discloses a conditioner head including a drive sleeve to which a hub is fixed, a backing plate connected to a body of a disk holder for holding a conditioning disk, and a plurality of sheet-like spokes that couple the hub and the backing plate to each other. The hub has a concave spherical portion, and the backing plate has a convex spherical portion with a radius equal to a radius of the concave spherical portion of the hub. The convex spherical portion is capable of being in sliding engagement with the concave spherical portion of the hub. The concave spherical portion of the hub and the convex spherical portion of the backing plate constitute a spherical bearing.
In the conditioner head disclosed in Japanese Laid-Open Patent Publication No. 2002-509811, the conditioning disk, the disk holder, and the backing plate are coupled to the drive sleeve through the sheet-like spokes which serve as a plate spring. Therefore, when the sheet-like spokes are plastically deformed, the conditioning disk cannot flexibly follow the polishing surface of the polishing pad. In particular, when the conditioner head is elevated, the conditioning disk, the disk holder, and the backing plate hang down from the sheet-like spokes, thus possibly causing the plastic deformation of the sheet-like spokes. Further, when the conditioner head is elevated, the concave spherical portion of the hub is separated from the convex spherical portion of the backing plate. As a result, a dressing load cannot be applied to the polishing surface, unless a load, which is larger than a total weight of the conditioning disk, the disk holder, and the backing plate, is applied to the conditioner head. Since dressing of the polishing surface cannot be performed within a low load range, a fine dressing-control cannot be performed.